Regulation of gene expression at the level of translation allows both cells and organisms to respond swiftly to physiological stress and changing environments. Indeed, differential translation of capped, polyadenylated mRNAs by eukaryotic ribosomes plays a critical role in numerous biological processes vital for human health, including normal cell growth, differentiation and development, learning and memory, and the response to environmental stress, including virus infection. Viral model systems have proven to be particularly useful in elaborating cellular translational control strategies because their successful replication is absolutely dependent upon viral mRNA translation by host ribosomes. This investigation utilizes a herpesvirus family member, human cytomegalovirus (HCMV), to probe the complex circuitry regulating mRNA translation. Although innocuous in most healthy individuals, HCMV is a widespread, opportunistic pathogen responsible for severe disease among the immunocompromised, including bone marrow and solid organ transplant recipients along with AIDS patients. In addition, congenital HCMV infection is the leading viral cause of birth defects in newborns. Unlike many viruses that impair cellular protein synthesis, polyribosome formation is stimulated and host mRNA translation proceeds uninterrupted in human cytomegalovirus (HCMV)-infected cells. In addition to stimulating ribosome biogenesis and host translation factor accumulation, HCMV selectively controls cellular mRNA translation. While translation of some host mRNAs stimulates HCMV replication, others exemplified by the translation factor eIF6 effectively restrict productive viral growth. Our long-term overall objectie is to understand the mechanism(s) through which HCMV manipulates the cellular translational machinery.to control viral replication. Based on our preliminary results, we hypothesize that HCMV-induced changes to the cellular translational machinery globally impact host and viral mRNA translation to properly regulate productive viral growth. Here, this hypothesis is tested in three specific aims designed to i) determine the role of eIF6 in HCMV infection biology and understand its anti-viral activity; ii) investigate how ribosome biogenesis controls HCMV replication; and iii) determine how ribosome recycling and translation termination factors control gene expression in infected cells and thereby impact HCMV infection biology. As mRNA translation is critical for both productive HCMV replication and reactivation from latency, our investigation is likely to reveal new strategies for interfering with viral replication and creatin weakened, attenuated strains useful for vaccine development. In addition, these studies will provide insight into basic mechanisms of translational control that are important in many human diseases, including cancer and diabetes, where the regulation of protein production is abnormal.